Welding blades to rotors

ABSTRACT

USING MAGNETIC FORCE UPSET WELDING TO FORM T-JOINTS BETWEEN DISSIMILAR THICKNESS PARTS. THIS TYPE OF RESISTANCE WELDING IS USED TO JOIN COMPRESSOR AND TURBINE PARTS THEREBY REDUCING THE WEIGHT AND COST OF A JET ENGINE.

United States Patent 1 Holko et al.

[1 1 3,745,300 [451 July 10,1973

1 1 WELDING BLADES TO ROTORS [75] Inventors: Kenneth H. Hoklo,Chulavista, Ca1if.; Thomas J. Moore, Berea, Ohio [73] Assignee: TheUnited States of America as represented by the Administrator of theNational Aeronautics and Space Administration, Washington, DC.

22 Filed: Apr. 16, 1971 21 App1.No.: 134,658

[52] U.S. Cl 219/107, 29/4975, 29/498, 219/62 [51] Int. C1 B231: 11/04[58] Field of Search 219/107, 102, 103, 219/104, 62, 99, 86, 78;29/4975, 498, 471.7,

[56] References Cited UNITED STATES PATENTS 1,248,813 12/1917 Costello..219/85 3,197,609 11/1971 Sommer 219/99 3,335,257 8/1967 Sakhamov eta1. 219/101 2,776,362 1/1957 Welch 219/86 2,231,480 2/1941 Pilger 219/99X 2,356,854 8/1944 Kirk 219/104 X 2,892,068 6/1959 Park et al 219/863,053,971 9/1962 Busse 219/107 3,047,712 7/1962 Morris 219/107 PrimaryExaminer-J. V. Truhe Assistant Examiner-L. A. Schutzman Attorney-N. T.Musial, G. E. Shoot and John R. Manning [5 7] ABSTRACT Using magneticforce upset we1ding to form T-joints between dissimilar thickness parts.This type of resistance welding is used to join compressor and turbineparts thereby reducing the weight and cost of a jet engine.

12 Claims, 5 Drawing Figures Patented July 10, 1973 3,745,300

FORCE OR CURRENT AMPLITUDE T'M INVENTORS E KENNETH H. HOLKO we. 5 THOMASJ. MOORE BY m [GA ATTORNEYS 1 WELDING BLADES TO ROTORS ORIGIN OF THEINVENTION The invention described herein was made by employees of theUnited States Government and may be manufactured and used by or for theGovernment for governmental purposes without the payment of anyroyalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention is concerned with producinghigh quality welded joints between sections of greatly differentthickness. The invention is particularly directed to welding compressorand turbine blades to rotors and discs.

Cast blades are customarily used in compressors and turbines. Theseblades have large bases which are received by mating slots in a drum.Thick drums are required so that the slots can be cut sufficiently largeto receive the blade bases. These factors increase the weight of a jetengine.

It has been proposed that compressor and turbine blades be joined torotors and disks by welding. However, most of the conventional weldingprocesses are not readily applicable to making a T-joint betweensections of greatly differing thicknesses because the thinner sectionsare heated more rapidly than the thicker ones. This produces poorquality welds because the heating is not concentrated at the interfaceformed at the T-joint junction.

Resistance welding has been suggested for these applications becausereduced.

5. A method as claimed in claim 1 including resistance heating isdeveloped at the interface where resistance is high. However, in theconventional mode of several cycles or more of current, there issufficient time for unequal heat dissipation to occur away from theinterface. Weak welds result from this insufficient interfacial heating.

Electron beam welding has also been suggested for attaching blades todrums. However, this procedure is both costly and complicated.

SUMMARY OF THE INVENTION These problems have been solved by theresistance welding process of the present invention which utilizes lowinitial electrode pressures, short welding times, and high weldingcurrent densities. These features are combined with the application of adelayed, rapidly rising magnetic force to concentrate the heating effectat the interface between the dissimilar thicknesses rather than in thebulk material.

OBJECTS OF THE INVENTION It is, therefore, an object of the presentinvention to provide a method of joining members of dissimilarthicknesses by resistance welding with little or no melting of theparent material.

Another object of the invention is to provide welded components for alow-cost, lightweight small jet aircraft engine. 7

A further object of the invention is to provide a resis tance weldingmethod for joining blades to rotors of lightweight jet engines.

These and other objects of the invention will be apparent from thespecification which follows and from the drawing wherein like numeralsare used throughout to identify like parts.

DESCRIPTION OF THE DRAWING In the drawing FIG. 1 is a vertical sectionshowing an unbeveled blade positioned in electrode tooling constructedin accordance with the invention for welding to a rotor;

FIG. 2 is a partial view, in elevation, of the inside surface of thetooling and is shown at a right angle to FIG. 1 illustrating analternate embodiment of the invention utilizing an insert in the end ofthe electrode tooling;

FIG. 3 is an enlarged view of the end of a blade which has been beveledprior to welding;

FIG. 4 is a simplified diagram of the magnetic force upset weldingequipment; and

FIG. 5 is a plot of typical current and force waves used in magneticforce upset welding.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing,there is shown in FIG. 1 a portion of a lightweight jet enginefabricated in accordance with the present invention. A plurality ofblades 10 are resistance welded to a rotor 12.

One of the blades is shown mounted in an electrode 14 prior to welding.This electrode forms tooling that must be capable of holding each blade10, cnducting high currents during operation, and transmitting upsetforces to the blade bases.

The electrode 14 is comprised of two sections 16 and 18 that areassembled by bolts and pins. Both sections 16 and 1,8 are of anelectrically conductive material, such as copper, that is capable ofconducting high currents. All bolts, pins, and locating buttons used inassembling the sections 16 and 18 are made of nonmagnetic material toprevent the establishment of magnetic fields which might deflect anddistrub current flow. All conducting surfaces of the electrode 14 aresilver plated to decrease the contact resistance and minimize pitting ofthe electrode from welding spatter.

A spacer 20 is positioned between the section 16 and 18 of the electrode14. The spacer contacts the upper edge of the blade 10 during thewelding operation. Spacers 20 of different thicknesses can be used tovary the extension of the blade 10 beyond the electrode 14. The spacer20 also transfers pneumatic and magnetic forces from the electrode 14 tothe blade. The spacer 20 is likewise of a nonmagnetic electricallyconducting material, such as copper.

The lower surface of the electrode section 16 which faces the rotor 12has a chamfered end portion 22 adjacent the blade 10. The electrodesection 18 has a similar chamfered end portion 24. The chamferedsurfaces 22 and 24 determine the contour of the welded blade base. Anangular contour at the joint between the blade 10 and the rotor 12reduces the stress concentration. A chamfer of 45 degrees has beensatisfactory to form a fillet at the junction of the blade 10 and rotor12.

It is also contemplated that a radius can be formed on the surfaces 22and 24 instead of the straight 45 degree chamfer shown in FIG. 1. Such aradiused chamfer will produce a similarly radiused fillet at the weld.

Referring now to FIG. 2 there is shown wedge shaped inserts 25 and 26 inthe electrode 14. These inserts are used to shape the current andheating patterns at the interface between the blade and the rotor. Theinserts 25 and 26 are preferably molybdenum and are properly posiitionedby a copper block 27. The inserts and the block are chamfered along thelower edge.

The lower edge of the blade that is to be welded to the rotor 12 extendsoutward from the lower edge of the electrode 14. This extension isextremely important in forming the weld at the proper location. Thisweld should be formed at the interface between the lower edge of theblade and the rotor surface. The extension is determined by thethickness of the spacer 20.

The lower edge of the blade 10 shown in FIG. 1 is substantially flat.The sides adjacent to this lower edge may be beveled at 28 and 30 asshown in FIG. 3. By beveling the blade 10 the initial contact thicknessis changed. Also by changing the bevel angle the shape of the final weldbetween the blade 10 and the rotor 12 is changed.

FIG. 4 is a simplified diagrammatic view of the apparatus for weldingthe blades 10 to the rotor 12 in accordance with the invention. Thisapparatus includes an upper platen 32 and a lower platen 34 shown inFIGS. 1 and 4. The upper platen 32 is movably mounted and carries theelectrode tooling 14. The lower platen 34 is mounted on a fixed base 36.The upper platen 32 is secured to the lower end of a reciprocable shaft38 having its upper end connected to the piston of an air cylinder 40.

A magnet armature 42 of a 120 hertz electromagnet is connected to theshaft 38 between the air cylinder 40 and the upper platen 32. A magnetstator 44 mounted below the armature 42 encircles the shaft 38. Thearmature 42 is adjustably mounted on the shaft 38 to enable the magnetair gap between the armature 42 and the stator 44 to be suitablyadjusted. A copper coil 46 is wrapped about the stator 44 and iselectrically connected to a secondary winding of a magnet transformer48. The primary winding of the transformer 48 is connected to magneticforce control equipment 50.,

A weld transformer 52 in a magnetic force upset welder has its primarywinding connected to weld voltage control equipment 54. The secondarywinding of the transformer 52 is connected to the upper platen 32 andlower platen 34. The weld voltage control equipment 54 varies thecurrent which passes through the electrode tooling 14.

In operation, the blade 10 is mounted in the electrode tooling 14 withthe upper platen 32 in a raised position. The space between the blade 10and the rotor 12 forms a break in the welding transformer secondary ofthe magnetic force upset welder.

The blade 10 is brought into light contact with the rotor as shown inFIG. 1 by moving the piston in the air cylinder 40. The faying surfacesof the blade 10 and rotor 12 are maintained in contact by pneumaticpressure transmitted through the spacer 20. The blade 10 is thenresistance welded to the rotor 12.

Referring now to FIG. 5 there is shown a plot of cur rent and forcewaves used in magnetic force upset welding. These waves are less thanone cycle of 60 hertz current and two cycles of 120 hertz force. Thesolid line 56 represents the force used during welding. As the fayingsurfaces of the blade and rotor are brought into contact, a pneumaticforce shown by the upward curved portion 58 is applied. This force ismaintained during the welding cycle.

A preheating current from the weld transformer 52 illustrated by thedotted line 60 is passed through the platens 32 and 34. This preheatcurrent is regulated by the weld voltage control 54. After a very shorttime delay of about 0.5 millisecond, caused by mechanical inertia in thewelding head, a preheat magnetic force is applied by the magnetic forcecontrol 50. This magnetic force is illustrated by the curved portion 62in the solid line. The small preheat half-cycle provides both macroandmicroalignment between the blades and rotor, incipient welding, and anincrease in interfacial temperature.

A welding current illustrated by the dotted line 64 is then passedthrough the blade and rotor. The welding half-cycle 64 provides the bulkof heating necessary in the formation of the weld. After a small weldingtime delay of about 1.5 milliseconds a weld magnetic force illustratedby the curve 66 in the solid line is applied by the magnetic forcecontrol 50. This magnetic force 66 is approximately 5 times thepneumatic force 58. This magnetic force 66 is used to upset the heatedblade and form a fillet at the chamfers 22 and 24 as the tooling 14moves from the position shown in FIG. 1 toward the rotor 12.

The magnetic force upset welding utilized in the present inventiondiffers from conventional resistance welding in that the forge force isapplied by a hertz electromagnet. The advantage is that the force-wavescan be timed in duration and phase shifted in relation to the'currenthalf-waves as illustrated in FIG. 5. The heating is more effectivelydeveloped and concentrated at the interface in this manner. By delayingthe initiation of the force half-wave after the initiation of thecurrent half-wave, the current flows through an interface between theblade 10 and the rotor 12 that is under low pressure and has highelectrical resistance. In this manner the resistance is high duringcurrent flow which increases the resistance heating at the interface.This is essential for welding unequal sections. The magnetic force upsetwelding utilizes high welding current densities and short current times.By way of example, the welding current density is generally greater thanl X 10 amperes per square inch, and the welding time is on the order ofone one hundred-twentieth second. The electromagnetic forging blow isprecisely timed with respect to the welding current.

A microscale liquid phase may be produced at the faying surfaces duringmagnetic force upset welding. Any molten material present tends to beforced out of the joint when the forging blow is applied. The absence ofmolten material at the joint assures minimum chemical segregation andminimum residual welding stress. Heat input to the joint is very low andis largely confined to the region immediately adjacent to the fayingsurfaces. This low heat input is quite desirable from a metallurgicalstandpoint.

Wave initiation, duration, and magnitude are dependent upon the settingof the weld control equipment 54. In the case of the magnetic forcewave, the magnet gap maybe adjusted as previously described to vary theforce magnitude at one control setting. By adusting this control settingand the magnet gap the time relation between the force initiation andthe current initiation is varied while the force magnitude is heldrelatively constant.

While the preferred embodiment of the invention has been described itwill be appreciated that various structural modifications may be madewithout departing from the spirit of the invention or the scope of thesubjoined claims. By way of example it is contemplated that theinvention may be used for positioning the blades on the rotor 12 priorto electron beam welding. After the blades have been resistance weldedto the rotor as previously described an electron beam weld is made atthe fillets.

What is claimed is:

1. A method of resistance welding members of differing thicknesses toeach other comprising the steps of moving one of said members intocontact with another member,

maintaining the faying surfaces of said one member and said other memberin contact by applying a substantially constant force to said contactingmembers, heating said contacting members at said faying surfaces to afirst predetermined temperature,

applying a first variable force to said contacting members during saidheating thereby providing macroalignment and microalignment between saidmembers, incipient welding, and an increase in inter-facial temperature,

heating said contacting members at said faying surfaces to a secondpredetermined temperature greater than said first predeterminedtemperature, and

applying a second variable force greater than said first variable forceto said contacting members during said heating to said secondpredetermined temperature to upset one of said contacting members andform a weld at the faying surfaces.

2. A method as claimed in claim 1 wherein the faying surfaces aremaintained in contact by a constant pneumatic force.

3. A method as claimed in claim 1 wherein said first and second variableforces applied to said heated members are magnetic forces.

4. A method as claimed in claim 1 including the step of beveling thesides of said one member adjacent to the edge thereof which contactssaid other member whereby the initial contact thickness is reduced.

5. A method as claimed in claim 1 including resistance heating saidcontacting members to said predetermined temperatures by passingpredetermined currents through said contacting members.

6. A method as claimed in claim 5 including passing a firstpredetermined current through said contacting members to heat the sameto said first predetermined temperature, and

applying said first variable force concurrent with the passage of saidfirst predetermined current.

7. A method as claimed in claim 5 including passing a secondpredetermined current through said contacting members to heat the sameto said second predetermined temperature, and

applying said second variable force concurrently with the passage ofsaid second predetermined current.

8. A method as claimed in claim 7 wherein the application of said secondvariable force is delayed after the start of the passage of said secondpredetermined current.

9. A method as claimed in claim 8 wherein the time delay is about 1.5milliseconds whereby the resistance is high during current flow toincrease the resistance heating at the interface.

10. A method as claimed in claim 9 wherein the second predeterminedcurrent has a density of about 1 X 10 amperes per square inch.

11. A method as claimed in claim 10 wherein said second magnetic forceis applied for about one one hundred-twentieth second.

12. A method as claimed in claim 1 including the step of making anelectron beam weld at the fillets after the members have been resistancewelded.

